The Experts below are selected from a list of 3972 Experts worldwide ranked by ideXlab platform
Mark K Transtrum - One of the best experts on this subject based on the ideXlab platform.
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vortex nucleation in superconductors within time dependent ginzburg landau theory in two and three dimensions role of surface defects and material inhomogeneities
Physical Review B, 2020Co-Authors: Alden Pack, Jared Carlson, Spencer Wadsworth, Mark K TranstrumAbstract:We use time-dependent Ginzburg-Landau theory to study the nucleation of vortices in type-II superconductors in the presence of both geometric and material inhomogeneities. The superconducting Meissner state is metastable up to a critical magnetic field, known as the Superheating field. For a uniform surface and homogeneous material, the Superheating transition is driven by a nonlocal critical mode in which an array of vortices simultaneously penetrate the surface. In contrast, we show that even a small amount of disorder localizes the critical mode and can have a significant reduction in the effective Superheating field for a particular sample. Vortices can be nucleated by either surface roughness or local variations in material parameters, such as ${T}_{c}$. Our approach uses a finite-element method to simulate a cylindrical geometry in two dimensions and a film geometry in two and three dimensions. We combine saddle-node bifurcation analysis along with a fitting procedure to evaluate the Superheating field and identify the unstable mode. We demonstrate agreement with previous results for homogeneous geometries and surface roughness and extend the analysis to include variations in material properties. Finally, we show that in three dimensions, surface divots not aligned with the applied field can increase the Superheating field. We discuss implications for fabrication and performance of superconducting resonant frequency cavities in particle accelerators.
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ginzburg landau theory of the Superheating field anisotropy of layered superconductors
Physical Review B, 2016Co-Authors: Danilo B Liarte, Mark K Transtrum, James P SethnaAbstract:We investigate the effects of material anisotropy on the Superheating field of layered superconductors. We provide an intuitive argument both for the existence of a Superheating field, and its dependence on anisotropy, for $\ensuremath{\kappa}=\ensuremath{\lambda}/\ensuremath{\xi}$ (the ratio of magnetic to superconducting healing lengths) both large and small. On the one hand, the combination of our estimates with published results using a two-gap model for ${\mathrm{MgB}}_{2}$ suggests high anisotropy of the Superheating field near zero temperature. On the other hand, within Ginzburg-Landau theory for a single gap, we see that the Superheating field shows significant anisotropy only when the crystal anisotropy is large and the Ginzburg-Landau parameter $\ensuremath{\kappa}$ is small. We then conclude that only small anisotropies in the Superheating field are expected for typical unconventional superconductors near the critical temperature. Using a generalized form of Ginzburg Landau theory, we do a quantitative calculation for the anisotropic Superheating field by mapping the problem to the isotropic case, and present a phase diagram in terms of anisotropy and $\ensuremath{\kappa}$, showing type I, type II, or mixed behavior (within Ginzburg-Landau theory), and regions where each asymptotic solution is expected. We estimate anisotropies for a number of different materials, and discuss the importance of these results for radio-frequency cavities for particle accelerators.
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Superheating field of superconductors within ginzburg landau theory
Physical Review B, 2011Co-Authors: Mark K Transtrum, Gianluigi Catelani, James P SethnaAbstract:We study the Superheating field of a bulk superconductor within Ginzburg-Landau theory, which is valid near the critical temperature. We calculate, as functions of the Ginzburg-Landau parameter $\ensuremath{\kappa}$, the Superheating field ${H}_{\mathrm{sh}}$ and the critical momentum ${k}_{c}$ characterizing the wavelength of the instability of the Meissner state to flux penetration. By mapping the two-dimensional linear stability theory into a one-dimensional eigenfunction problem for an ordinary differential equation, we solve the problem numerically. We demonstrate agreement between the numerics and analytics, and show convergence to the known results at both small and large $\ensuremath{\kappa}$. We discuss the implications of the results for superconducting rf cavities used in particle accelerators.
James P Sethna - One of the best experts on this subject based on the ideXlab platform.
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ginzburg landau theory of the Superheating field anisotropy of layered superconductors
Physical Review B, 2016Co-Authors: Danilo B Liarte, Mark K Transtrum, James P SethnaAbstract:We investigate the effects of material anisotropy on the Superheating field of layered superconductors. We provide an intuitive argument both for the existence of a Superheating field, and its dependence on anisotropy, for $\ensuremath{\kappa}=\ensuremath{\lambda}/\ensuremath{\xi}$ (the ratio of magnetic to superconducting healing lengths) both large and small. On the one hand, the combination of our estimates with published results using a two-gap model for ${\mathrm{MgB}}_{2}$ suggests high anisotropy of the Superheating field near zero temperature. On the other hand, within Ginzburg-Landau theory for a single gap, we see that the Superheating field shows significant anisotropy only when the crystal anisotropy is large and the Ginzburg-Landau parameter $\ensuremath{\kappa}$ is small. We then conclude that only small anisotropies in the Superheating field are expected for typical unconventional superconductors near the critical temperature. Using a generalized form of Ginzburg Landau theory, we do a quantitative calculation for the anisotropic Superheating field by mapping the problem to the isotropic case, and present a phase diagram in terms of anisotropy and $\ensuremath{\kappa}$, showing type I, type II, or mixed behavior (within Ginzburg-Landau theory), and regions where each asymptotic solution is expected. We estimate anisotropies for a number of different materials, and discuss the importance of these results for radio-frequency cavities for particle accelerators.
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Superheating field of superconductors within ginzburg landau theory
Physical Review B, 2011Co-Authors: Mark K Transtrum, Gianluigi Catelani, James P SethnaAbstract:We study the Superheating field of a bulk superconductor within Ginzburg-Landau theory, which is valid near the critical temperature. We calculate, as functions of the Ginzburg-Landau parameter $\ensuremath{\kappa}$, the Superheating field ${H}_{\mathrm{sh}}$ and the critical momentum ${k}_{c}$ characterizing the wavelength of the instability of the Meissner state to flux penetration. By mapping the two-dimensional linear stability theory into a one-dimensional eigenfunction problem for an ordinary differential equation, we solve the problem numerically. We demonstrate agreement between the numerics and analytics, and show convergence to the known results at both small and large $\ensuremath{\kappa}$. We discuss the implications of the results for superconducting rf cavities used in particle accelerators.
Takayuki Kubo - One of the best experts on this subject based on the ideXlab platform.
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field limit and nano scale surface topography of superconducting radio frequency cavity made of extreme type ii superconductor
Progress of Theoretical and Experimental Physics, 2015Co-Authors: Takayuki KuboAbstract:The field limit of superconducting radio-frequency cavity made of type II superconductor with a large Ginzburg-Landau parameter is studied with taking effects of nano-scale surface topography into account. If the surface is ideally flat, the field limit is imposed by the Superheating field. On the surface of cavity, however, nano-defects almost continuously distribute and suppress the Superheating field everywhere. The field limit is imposed by an effective Superheating field given by the product of the Superheating field for ideal flat surface and a suppression factor that contains effects of nano-defects. A nano-defect is modeled by a triangular groove with a depth smaller than the penetration depth. An analytical formula for the suppression factor of bulk and multilayer superconductors are derived in the framework of the London theory. As an immediate application, the suppression factor of the dirty Nb processed by the electropolishing is evaluated by using results of surface topographic study. The estimated field limit is consistent with the present record field of nitrogen-doped Nb cavities. For a further improvement of field, a surface processing technology that can realize a surface with a smaller slope-angle distribution is necessary. Suppression factors of surfaces of other bulk and multilayer superconductors, and those after various surface processing technologies can also be evaluated by using the formula.
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field limit and nano scale surface topography of superconducting radio frequency cavity made of extreme type ii superconductor
arXiv: Accelerator Physics, 2014Co-Authors: Takayuki KuboAbstract:The field limit of superconducting radio-frequency cavity made of type II superconductor with a large Ginzburg-Landau parameter is studied with taking effects of nano-scale surface topography into account. If the surface is ideally flat, the field limit is imposed by the Superheating field. On the surface of cavity, however, nano-defects almost continuously distribute and suppress the Superheating field everywhere. The field limit is imposed by an effective Superheating field given by the product of the Superheating field for ideal flat surface and a suppression factor that contains effects of nano-defects. A nano-defect is modeled by a triangular groove with a depth smaller than the penetration depth. An analytical formula for the suppression factor of bulk and multilayer superconductors are derived in the framework of the London theory. As an immediate application, the suppression factor of the dirty Nb processed by the electropolishing is evaluated by using results of surface topographic study. The estimated field limit is consistent with the present record field of nitrogen-doped Nb cavities. Suppression factors of surfaces of other bulk and multilayer superconductors, and those after various surface processing technologies can also be evaluated by using the formula.
A. I. Schastlivtsev - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic efficiency of geothermal power stations with hydrogen steam Superheating
Thermal Engineering, 2010Co-Authors: S. P. Malyshenko, A. I. SchastlivtsevAbstract:Results from studying the use of hydrogen steam Superheating for geothermal plants by means of a thermodynamic analysis are presented. The optimal steam Superheating range is determined within which the maximal efficiency of a geothermal plants is achieved with the minimal cost for installing additional equipment.
Yinshi Li - One of the best experts on this subject based on the ideXlab platform.
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thermal load and bending analysis of heat collection element of direct steam generation parabolic trough solar power plant
Applied Thermal Engineering, 2017Co-Authors: Lu Li, Jie Sun, Yinshi LiAbstract:Abstract The reliability of heat collection element (HCE) in parabolic trough collector (PTC) system is of importance to the solar thermal energy harvesting. The present work proposes the 2D-finite volume method (FVM) and 3D-finite element volume (FEM) coupled model to conduct the thermal load and bending analysis of the HCE of direct-steam-generation (DSG) PTC solar power plant. The emphasis is focused on the evaporation and Superheating stages of a DSG loop in re-circulation mode due to the presence of the phase-change process and the relatively lower heat transfer performance, respectively. It is found that the thermal deflection is far less than 1 cm for a 4-m HCE in the evaporation stage. However, in the Superheating stage with DNI = 1000 W m−2 (DNI being the direct normal irradiance), the circumferential temperature difference and the deflection of a 4-m HCE can reach up to 48 °C and 2.16 cm, respectively. It should be pointed out, based on the present work, that the non-uniform heating and local overheating issues exist in the evaporation and Superheating stages, respectively, the latter of which seems more serious and potentially causes damage.
